The National Republican Congressional Committee raised $6 million in May, according to an NRCC aide — $1.3 million less than the Democratic Congressional Campaign Committee raised in the same period. The NRCC's monthly haul brings its total cash on hand to $35.2 million — $10.7 million less than what the DCCC has in the bank.

Part of the DCCC's fundraising success is rooted in their online fundraising. The DCCC brought in $2.3 million in May from its online fundraising operation, a large chunk of the committee's $7.3 million monthly haul.

The committees use these funds to support candidates in the fall midterms.

Last month, the DCCC reserved $43.5 million in television airtime for the fall, while the NRCC reserved $30 million . The committees are likely to add to those totals as the cycle progresses.